Asyncronous spy assertions with python-doublex

Sometimes interaction among your SUT class and their collaborators does not meet a synchronous behavior. That may happen when the SUT perform collaborator invocations in a different thread, or when the invocation pass across a message queue, publish/subscribe service, etc.

due to the called() assertion may happen before the write() invocation, but not always.

You may be tempted to put a sleep before the assertion, but this is a bad solution. A right way to solve that issue is to use something like a barrier. The threading.Event class may be used as a barrier. See this new test version:

The spy.write.attach() is part of the doublex testing framework and provides stub-observers. That is, a way to run arbitrary code when stubbed methods are called.

That works because the called() assertion is performed only when the spy release the barrier. It the write() invocation never happen, the barrier.wait() continues after 1 second and the test fail, as must do. When all is right, the barrier waits just the required time.

Well, this mechanism is a doublex builtin in the last release (1.5.1) and provide the same behavior in a clearer way. The next is functionally equivalent to the second test version above: